feat: implements block height check in PrepareProposal to avoid unexpected errors at height 1 (backport #2233)

[mergify]

This is an automatic backport of pull request #2233 done by Mergify.
Cherry-pick of e2b154d has failed:

On branch mergify/bp/v1.x/pr-2233
Your branch is up to date with 'origin/v1.x'.

You are currently cherry-picking commit e2b154d.
  (fix conflicts and run "git cherry-pick --continue")
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Changes to be committed:
	modified:   app/prepare_proposal.go

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   app/test/block_production_test.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[codecov-commenter]

Codecov Report

Merging #2423 (15a9d87) into v1.x (6639c1a) will decrease coverage by 0.04%.
Report is 1 commits behind head on v1.x.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             v1.x    #2423      +/-   ##
==========================================
- Coverage   20.52%   20.49%   -0.04%     
==========================================
  Files         138      138              
  Lines       15761    15788      +27     
==========================================
  Hits         3235     3235              
- Misses      12219    12246      +27     
  Partials      307      307              

Files Changed	Coverage Δ
app/prepare_proposal.go	0.00% <0.00%> (ø)
test/util/testnode/config.go	0.00% <0.00%> (ø)